1. Field of the Invention
This invention relates to a circuit for synchronizing the oscillation of a pulsed oscillator with a reference oscillation of comparatively low amplitude.
2. Description of the Prior Art
In radar systems, particularly in secondary radar systems, in which pulsed oscillators are employed, there are certain requirements for a constant frequency, which requirements can be satisfied only partially be crystal control. The expense for multiplying the crystal oscillation and amplification of the same to the required transmitting power is too great, particularly for small devices. On the other hand, a free running oscillator which can deliver the required transmitting power is, indeed, very simply constructed, but the same is not sufficiently constant in frequency. If crystal-control of a low power transmitting frequency is already present in a local oscillator, such as in the case of secondary radar systems, for example, then there is the possibility of synchronizing the pulsed oscillator to this oscillation with little expense, whereby, however, the oscillator frequency must already be captured when the oscillator begins to oscillate.
The fixed frequency synchronization of an oscillator with a reference oscillation by means of a phase discriminator and a controlled reactance, for example capacitance diodes, is known in the art. However, special circuits are required which sweep the oscillator frequency for the purpose of capturing that frequency, whereby the frequency is fixed upon sweeping the nominal frequency. However, sweeping lasts for a comparatively long period and is therefore unusable in the pulsed oscillator. If both frequencies are very similar, capturing will occur by itself. However, this cannot be assumed.